House electric



June 10, 1930. J. c. wooDsoN `1,763,117

ELECTRIC HEATING UNIT Filed Oct. 10, 1925 //IIIIIIIIIIIII v. v agg N VENTOR V/'mes C MM50@ UM'IED "STATES Patented `lune 10, 1930iwi'rlala'l"v OFFICE JAMES C. wooDSoN, OE EAST PITTSBURGH, PENNSYLVANIA,ASSI''LNoR To WESTING- HOUSE ELECTRIC 'sa MANUFACTURING COMPANY, ACORPORATION OE PENNSYL- 4 vANIA ELECTRIC HEATING UNIT Application sledoctober 1o, 1925. serialfNo. 61,683.

' My invention relates to electric heating units :and particularly tounits in whichthe resistor member is entirely inclosed.

An object of my inventionis to provide a heating unit that Shall haveits heating element inclosed and protectedfrom the air and which shallhave high-thermal conductivity, thereby prolonging the lift of theheating element. 'Y y Another object' of my inventionl isto prol vide aheating unit that-may be easily manufactured, which shallbe durable andwhich shall have its heating element protected from en agement withforeign'A bodies or fluids.

n the accompanying drawings,

Figure 1 is a view, in longitudinal section, of a vheating unitembodying my invention,

Fig. 2 is a view in longitudinal section of a device embodying amodfiedform of my invention, 2 1

Fig. 3 is a view incross' section of fthe device, illustrated inFig.l2,-and Y Fig. 4 is a view in longitudinal sectionof a furthermodification Of the device embodyinglmy'invention. y eferring more-particularly lto`fF-ig.1,'fa heating unit 11 comprises a presbapedresistor element'12 disposed within pulverulent, electricallynon-conducting material 13. The material 13 is surrounded vby a sheet 14bent in the form of a cylinder or tube, of expan- Sively oXidiZablemetal'which, in turn, is in-A closed within a cylinder of suitable metal15,

. The ends of the resistor element 12 'are attached to terminals 16,only one of which is shown, which, in turn, is registered with a closuremember 17 that is of suitable dimensions to fit snugly within thetubularmem ber 14.

The Dulverulent material 13 which is sub# stantially electricallynon-conducting, may be, for example, magnesium oxide in powderedf'orm oralundum powder. v In constructing the heating unit'illustrated in 1, itis desirable to place the cylinder 14` ofexpansively oxidizablematerial, such as magnesium, within the cylinder 15 and then to locatethe preshaped resistor'element 12 centrally within the enclosure-thusformed. The alundum powder or the magnesium Oxide powder may then bepoured into the tube so as to completely -surround the resistor element12 therebysupporting the same in its pre-shaped form. The oxide oralundum powder 13 Amay be compacted inplace, whereby good mechanicalcontactis made between the material 13 and the element 12.

The provisionof thevsleeve or'cylinder 14 insures-that the heat will beconducted away from the resistor element' 12 to the'surface of the tube15 by reason of the eliicient thermally conductive relation between theassociated parts when' the sleevehas` been expanded by oxidation inthemann'er described below. i f

A small clearance is left between the inner diameter of thecylinder 15and the outer diameter ofthe Acylinder 14, whereby'steamat asuitable-.pressure may l'be forced through to change the magnesium metalofthe tube 14 to magnesium'o'xide. "It is characteristic ofmagnesiummeta'l, when thus 'treated with 'steam to'= changeto magnesiumoxide and to expand substantially to'200'% of its original dimensions.Since the magnesium is located within-a' strong tube, as illustrated bythe member 15 in Fig. 1, a very high radial pressure will-result betweenthe granular material 13 and the outer Vtube 15, thereby effecting highthermal conductivity from the element 12 to the surface of the member15. As the magnesium oxide is an electric insulator, the resistor 12 iseffectively insulated from the tube 1 5.

The closure member 17, which is made of an electric-insulating material,is located within the magnesium tube 14 before the oXidation thereoftakes lace. Since the material 14 expands on belngoxidized, the member17 is held firmly in position in the heating unit 11l- In order thatcomplete oxidation of the metal tube v14* may take place, I mayernploythe construction of Figs. 2 and 3 in which an oxidizing agent 18,`suchas red lead, is in serted between the granular material 13 and amagnesium tube 19 having longitudinal slots or grooves 21 therein. Onheating with steam the magnesium nearest the inner surface of thecylinder 15 will be in more direct Contact with the steam than the innersurface of the magnesium tube 19, but as the temperature of themagnesium is raised to a high degree as a result of the temperature 5 ofthe steam, oxygen will he liberated from the oxidizin agent 18 tooxidize the inner surface of t e magnesium tube 19, thereby causing acomplete transformation of magnesiumvmetal to magnesium oxide.

lAsshown in Fig. 3 which shows the initial positionsof the va riouselements before treatment, the tube 19 has a plurality of projections 20on its outer circumference that form longitudinal slots therein. Theseprojections may be produced by drawinvf a tube of magnesium metalthrough a suitable die. The grooves 21 intervening between theprojections'20 extend longitudinally of the heating unit so as tofacilitate -the passage of steam therethrough. These .grooves need notnecessarily extend longitudinally of the heating unit 11, as they mayextend helically -along the outer surface of the member 14.

Although I have not illustrated all of the methods by which themagnesium metal 14 may be inserted within the tube l5, there are othermethods by which the metal 14 may be disposed therein. 'F or example,magnesium metal in the form of narrow ribbon of suitable thickness niaybe wound in the form of a helixv22 -as illustrated .in Fig. 4, and theninserted within the tube 15, whereby substantially the same result isobtained.

The Idevice embodying my invention pro- 5 ductor inclosed within twocylinders, the

innercylinder being an expansively oxidizable material. The conductor iscentrally located in the opening withinthe cylinders and pulverulent orgranular material is compacted therearound. On oxidizing the expansivelyoxidizable material, the granular material is compacted and the outercylinder is firmly held in operative position and in good thermalconductive relation with the conductor by reason of the expansion of theoxidizable material.

The device embodying my invention may be manufactured in various sizesand shapes, as for. instance in substantially circular tubes having anouter diameter of about 3/8 inches and of any desired length. Largersizes may employ outer cylindrical members of other than circular shapein cross-section such as rectangular or oval.

Various modifications of my invention may be .made without departingfrom the spirit and the scope thereof. I desire, therefore, that onlysuch limitations shall be placed thereon as shall be imposed by theprior `art and the appended claims.

I claim as my invention:

1. In an electric-heating unit, in combination, an electric-resistanceconductor having 65 terminals at the ends thereof, granular elecvides aheating unit which comprises a con,

trically non-conducting material disposed therearound, a casinginclosing said granular material, and electric-insulating materialdisposed between said casing and the granular material comprisingexpansively oxidized magnesium oxidefor tightly compacting the granularmaterial, for maintaining the terminals firmly in operative relationwithin the casing and for effecting high thermally-.conductive relationbetween 'said .electric con-v ductor and said casing.

2. In an electric-heating device, in combination,"a helically-woundelectric resistor .having terminals at. the ends thereof, pulverulentelectrically non-conducting material disposed -therearound to, firmlysupport said conductor and to be in thermal contact therewith, a metalcasing inclosing said pulverulent material, andelectric-insulating'material disposed between said-:casing and-thepulverulent material com risingexpansively oxidized-magnesium =oXi e'for tightlyxcomn pacting the pulverulent material within the casing,for maintaining the terminals firmly in operative relation within the clinder and for effecting high thermal conduction vbeween said electricconductorv .and said cylin 3. The method of making a Atubularzheati ingunit, which .comprises locating asubstantially-tubular memberiofmetallic magnesium within a metal casing, locatinga Aresistor elementywithin said :tubular member, filling the space with pulverulentelectricinsulating material, and then subjecting the assembled elementslto. the action of steam lto expansively oxidize the magnesium intomagnesium 0X- ide to .tightlycompact the lling within the outer casing.

'4. The method of making a .tubular heating unit which compriseslocating -an exten nally longitudinally grooved cylinder of metallicmagnesium in .an outer metal casing, locating a .resistor member in.theoylinder, filling the vspace within the cylinderwith a pulverulentelectric-insulating material and subjecting said elements to the actionof steam to expansivelyoxidize the magnesium into magnesium oxide-totightly compact the filling in the casing.

5. The method of making a tubular heating unit, which comprises locatinga cylinn drical member of metallic magnesium in an outer metal casing,locating a preformed resistor member having a terminal member connectedtheretoin said cylindrical member, locating a bushing-ofelectric-insulating material within the cylindrical member and aroundthe terminal member,lling the cylindrical member with a pulverulent-electric-insulating material, and then subject ing the assembledelements to the action of steam to compact the pulverulent .material andtightly -hold the bushing in the metal casing.

6. The method of making a tubular heating unit, which comprises locatinga substantially tubular member of metallic magnesium Within asubstantially co-eXtensive metal casing, locating a preformed resistormember centrally of said tubular member of magnesium, placing a fillingof pulverulent electric-insulating material in the tubular member,compacting said filling, and then subjecting the assembled elements tothe action of steam to expansively oxidize the magnesium into magnesiumoxide to tightly compact the filling Within the casing.

In testimony whereof, I have hereunto subscribed my name this 28th dayof September,

JAMES C. WOODSON.

